Dynamic spect camera

ABSTRACT

A method of reconstruction of a radioactive emission image. The method comprises providing a first system of voxels for a region of interest, obtaining radioactive-emission data from the region of interest, performing a first reconstruction, based on the radioactive-emission data and the first system of voxels, to obtain a first image, correcting the first system of voxels, by aligning voxel boundaries with object boundaries, based on the first image; thus obtaining a second system of voxels, and performing a second reconstruction, based on the radioactive-emission data and the second system of voxels, thus obtaining a second image.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/084,559 filed on Nov. 26, 2008, which is a National Phase of PCTApplication No. PCT/IL2006/001291 having International Filing Date ofNov. 9, 2006.

PCT Application No. PCT/IL2006/001291 is a continuation-in-part (CIP) ofPCT Application Nos. PCT/IL2006/000840 and PCT/IL2006/000834, both filedon Jul. 19, 2006, PCT Application No. PCT/IL2006/000562, filed on May11, 2006, PCT Application No. PCT/IL2006/000059, filed on Jan. 15, 2006,PCT Application No. PCT/IL2005/001215, filed on Nov. 16, 2005, and PCTApplication No. PCT/IL2005/001173, filed on Nov. 9, 2005.

PCT Application No. PCT/IL2006/001291 also claims the benefit ofpriority from U.S. Provisional Patent Application No. 60/816,970, filedon Jun. 28, 2006, U.S. Provisional Patent Application Nos. 60/800,846and 60/800,845, both filed on May 17, 2006, U.S. Provisional PatentApplication No. 60/799,688, filed on May 11, 2006, U.S. ProvisionalPatent Application No. 60/763,458, filed on Jan. 31, 2006, U.S.Provisional Patent Application No. 60/754,199, filed on Dec. 28, 2005,U.S. Provisional Patent Application Nos. 60/750,597 and 60/750,334, bothfiled on Dec. 15, 2005, U.S. Provisional Patent Application No.60/750,287, filed on Dec. 13, 2005, and U.S. Provisional PatentApplication No. 60/741,440, filed on Dec. 2, 2005.

PCT Application No. PCT/IL2006/001291 also claims the benefit ofpriority from Israel Patent Application No. 172349, filed on Nov. 27,2005.

PCT Application No. PCT/IL2005/001173 is a continuation-in-part (CIP) ofPCT Application Nos. PCT/IL2005/000575, and PCT/IL2005/000572, bothfiled on Jun. 1, 2005, and PCT Application No. PCT/IL2005/000048, filedon Jan. 13, 2005.

PCT Application No. PCT/IL2005/001173 also claims the benefit ofpriority from U.S. Provisional Patent Application Nos. 60/720,652 and60/720,541, both filed on Sep. 27, 2005, U.S. Provisional PatentApplication No. 60/720,034, filed on Sep. 26, 2005, U.S. ProvisionalPatent Application No. 60/702,979, filed on Jul. 28, 2005, U.S.Provisional Patent Application Nos. 60/700,753 and 60/700,752, bothfiled on Jul. 20, 2005, U.S. Provisional Patent Application Nos.60/700,318, 60/700,317, and 60/700,299, filed on Jul. 19, 2005, U.S.Provisional Patent Application No. 60/691,780, filed on Jun. 20, 2005,U.S. Provisional Patent Application No. 60/675,892, filed on Apr. 29,2005, U.S. Provisional Patent Application No. 60/648,690, filed on Feb.2, 2005, U.S. Provisional Patent Application No. 60/648,385, filed onFeb. 1, 2005, U.S. Provisional Patent Application No. 60/640,215, filedon Jan. 3, 2005, U.S. Provisional Patent Application No. 60/636,088,filed on Dec. 16, 2004, U.S. Provisional Patent Application No.60/635,630, filed on Dec. 14, 2004, U.S. Provisional Patent ApplicationNo. 60/632,515, filed on Dec. 3, 2004, U.S. Provisional PatentApplication No. 60/632,236, filed on Dec. 2, 2004, U.S. ProvisionalPatent Application No. 60/630,561, filed on Nov. 26, 2004, U.S.Provisional Patent Application No. 60/628,105, filed on Nov. 17, 2004,and U.S. Provisional Patent Application No. 60/625,971, filed on Nov. 9,2004.

PCT Application No. PCT/IL2005/001173 also claims the benefit ofpriority from Israel Patent Application No. 171346, filed on Oct. 10,2005.

PCT Application No. PCT/IL2005/000575 claims the benefit of priorityfrom U.S. Provisional Patent No. 60/575,369, filed on Jun. 1, 2004.

U.S. patent application Ser. No. 12/084,559 is also acontinuation-in-part (CIP) of U.S. patent application Ser. No.11/034,007, filed on Jan. 13, 2005, now U.S. Pat. No. 7,176,466, issuedon Feb. 13, 2007, which claims the benefit of priority from U.S.Provisional Patent Application No. 60/535,830, filed on Jan. 13, 2004.

The contents of the above Applications are all incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates SPECT nuclear imaging, and particularly,to systems, methods, and cameras forsingle-photon-emission-computed-tomography, in list mode, withsensitivity which meets, even outperforms that of PET, in terms of speedand spatial resolution, and with a high spectral resolution notavailable in PET.

BACKGROUND OF THE INVENTION

Radionuclide imaging aims at obtaining an image of a radioactivelylabeled substance, that is, a radiopharmaceutical, within the body,following administration, generally, by injection. The substance ischosen so as to be picked up by active pathologies to a different extentfrom the amount picked up by the surrounding, healthy tissue inconsequence, the pathologies are operative as radioactive-emissionsources and may be detected by radioactive-emission imaging. A pathologymay appear as a concentrated source of high radiation, that is, a hotregion, as may be associated with a tumor, or as a region of low-levelradiation, which is nonetheless above the background level, as may beassociated with carcinoma.

A reversed situation is similarly possible. Dead tissue has practicallyno pick up of radiopharmaceuticals, and is thus operative as a coldregion.

The mechanism of localization of a radiopharmaceutical in a particularorgan of interest depends on various processes in the organ of interestsuch as antigen-antibody reactions, physical trapping of particles,receptor site binding, removal of intentionally damaged cells fromcirculation, and transport of a chemical species across a cell membraneand into the cell by a normally operative metabolic process. A summaryof the mechanisms of localization by radiopharmaceuticals is found inhttp://www.lunis.luc.edu/nucmed/tutorial/radpharm/i.htm.

The particular choice of a radionuclide for labeling antibodies dependsupon the chemistry of the labeling procedure and the isotope nuclearproperties, such as the number of gamma rays emitted, their respectiveenergies, the emission of other particles such as beta or positrons, theisotope half-life, and the decay scheme.

In PET imaging, positron emitting radio-isotopes are used for labeling,and the imaging camera detects coincidence photons, the gamma pair of0.511 Mev, traveling in opposite directions. Each coincident detectiondefines a line of sight, along which annihilation takes place. As such,PET imaging collects emission events, which occurred in an imaginarytubular section enclosed by the PET detectors. A gold standard for PETimaging is PET NH₃ rest myocardial perfusion imaging with N-13-ammonia(NH₃), at a dose level of 740 MBq, with attenuation correction. Yet,since the annihilation gamma is of 0.511 Mev, regardless of theradio-isotope, PET imaging does not provide spectral information, anddoes not differentiate between radio-isotopes.

In SPECT imaging, primarily gamma emitting radio-isotopes are used forlabeling, and the imaging camera is designed to detect the actual gammaemission, generally, in an energy range of approximately 11-511 KeV.Generally, each detecting unit, which represents a single image pixel,has a collimator that defines the solid angle from which radioactiveemission events may be detected.

Because PET imaging collects emission events, in the imaginary tubularsection enclosed by the PET detectors, while SPECT imaging is limited tothe solid collection angles defined by the collimators, generally, PETimaging has a higher sensitivity and spatial resolution than does SPECT.Therefore, the gold standard for spatial and time resolutions in nuclearimaging are defined for PET. For example, there is a gold standard forPET imaging for at rest myocardial perfusion with N-13-ammonia (NH₃), ata dose of 740 MBq with attenuation correction.”

Conventional SPECT cameras generally employ an Anger camera, in which asingle-pixel scintillation detector, such as NaI(Tl), LSO, GSO, CsI,CaF, or the like, is associated with a plurality of photomultipliers.Dedicated algorithms provide a two dimensional image of thescintillations in the single pixel scintillation detector. There areseveral disadvantages to this system, for example:

1. the dedicated algorithms associated with the single pixel cannotreach the accuracy of a two-dimensional image of a plurality of singlepixel detectors;

2. the single-pixel detector is a rigid unit, which does not have theflexibility of motion of a plurality of small detectors, each withindependent motion; and

3. a single hot spot may cause the single pixel detector of the Angercamera to saturate, whereas when a plurality of single pixel detectorsis employed, saturation is localized to a few pixels and does not affectthe whole image.

Other SPECT cameras which employ a plurality of single pixel detectorsare also known.

U.S. Pat. No. 6,628,984, to Weinberg, issued on Sep. 30, 2003 andentitled, “Hand held camera with tomographic capability,” describes atomographic imaging system, which includes a moveable detector ordetectors capable of detecting gamma radiation; one or more positionsensors for determining the position and angulation of the detector(s)in relation to a gamma ray emitting source; and a computational devicefor integrating the position and angulation of the detector(s) withinformation as to the energy and distribution of gamma rays detected bythe detector and deriving a three dimensional representation of thesource based on the integration. A method of imaging a radiationemitting lesion located in a volume of interest also is disclosed.

U.S. Pat. No. 6,242,743, to DeVito, et al., issued on Jun. 5, 2001 andentitled, “Non-orbiting tomographic imaging system,” describes atomographic imaging system which images ionizing radiation such as gammarays or x rays and which: 1) can produce tomographic images withoutrequiring an orbiting motion of the detector(s) or collimator(s) aroundthe object of interest, 2) produces smaller tomographic systems withenhanced system mobility, and 3) is capable of observing the object ofinterest from sufficiently many directions to allow multipletime-sequenced tomographic images to be produced. The system consists ofa plurality of detector modules which are distributed about or aroundthe object of interest and which fully or partially encircle it. Thedetector modules are positioned close to the object of interest therebyimproving spatial resolution and image quality. The plurality ofdetectors view a portion of the patient or object of interestsimultaneously from a plurality of positions. These attributes areachieved by configuring small modular radiation detector withhigh-resolution collimators in a combination of application-specificacquisition geometries and non-orbital detector module motion sequencescomposed of tilting, swiveling and translating motions, and combinationsof such motions. Various kinds of module geometry and module orcollimator motion sequences are possible, and several combinations ofsuch geometry and motion are shown. The geometric configurations may befixed or variable during the acquisition or between acquisitionintervals. Clinical applications of various embodiments of U.S. Pat. No.6,242,743 include imaging of the human heart, breast, brain or limbs, orsmall animals. Methods of using the non-orbiting tomographic imagingsystem are also included.

U.S. Pat. No. 5,939,724, to Eisen, et al., issued on Aug. 17, 1999, andentitled, “Light weight-camera head and -camera assemblies containingit,” describes a light weight gamma-camera head and assemblies and kitswhich embody it. The gamma-camera head has a detector assembly whichincludes an array of room temperature, solid state spectroscopy gradedetectors each associated with a collimator and preamplifier, whichdetectors and associated collimators and preamplifiers are arranged inparallel rows extending in a first direction and suitably spaced fromeach other in a second direction normal to the first direction, each ofthe parallel detector rows holding a plurality of detectors. The headmay optionally have an electric motor for moving the detector in thesecond direction and optionally also in the first direction, eitherstepwise or continuously.

U.S. Pat. No. 6,525,320, to Juni, issued on Feb. 25, 2003, and entitled,Single photon emission computed tomography system, describes a singlephoton emission computed tomography system, which produces multipletomographic images of the type representing a three-dimensionaldistribution of a photon-emitting radioisotope. The system has a baseincluding a patient support for supporting a patient such that a portionof the patient is located in a field of view. A longitudinal axis isdefined through the field of view. A detector module is adjacent thefield of view and includes a photon-responsive detector. The detector isan elongated strip with a central axis that is generally parallel to thelongitudinal axis. The detector is operable to detect if a photonstrikes the detector. The detector can also determine a position alongthe length of the strip where a photon is detected. A photon-blockingmember is positioned between the field of view and the detector. Theblocking member has an aperture slot for passage of photons aligned withthe aperture slot. The slot is generally parallel to the longitudinalaxis. A line of response is defined from the detector through theaperture. A displacement device moves either the detector module or thephoton-blocking member relative to the other so that the aperture isdisplaced relative to the detector and the line of response is sweptacross at least a portion of the field of view.

U.S. Pat. No. 6,271,525, to Majewski, et al., issued on Aug. 7, 2001,and entitled, “Mini gamma camera, camera system and method of use,”describes a gamma camera, which comprises essentially and in order fromthe front outer or gamma ray impinging surface: 1) a collimator, 2) ascintillator layer, 3) a light guide, 4) an array of position sensitive,high resolution photomultiplier tubes, and 5) printed circuitry forreceipt of the output of the photomultipliers. There is also described,a system wherein the output supplied by the high resolution, positionsensitive photomultipiler tubes is communicated to: a) a digitizer andb) a computer where it is processed using advanced image processingtechniques and a specific algorithm to calculate the center of gravityof any abnormality observed during imaging, and c) optional imagedisplay and telecommunications ports.

U.S. Pat. No. 6,271,524, to Wainer, et al., issued on Aug. 7, 2001 andentitled, “Gamma ray collimator,” describes a gamma ray collimatorassembly comprising collimators of different gamma ray acceptanceangles. For example, the acceptance angle of a first collimator may bebetween 0.2 and 5 degrees, and the acceptance angle of a secondcollimator may be between about 5 and 30 degrees.

U.S. Pat. No. 6,212,423, to Krakovitz, issued on Apr. 3, 2001 andentitled, “Diagnostic hybrid probes,” describes a hybrid nuclear andultrasonic probe, comprising a cylindrical outer casing surrounding anuclear probe, which comprises two scintillator plates intersectingperpendicularly, each of the scintillator plates having a plurality ofparallel collimators; and an ultrasonic probe situated between saidcasing at the intersection of said scintillator plates.

List mode data acquisition is known in PET studies, and enables thedetermination of coincidence. It relates to recording every radiationevent together with data pertinent to that event, which includes:

i. the time the radiation event impinged upon a detector pixel, withrespect to a clock, with respect to a time bin, or with respect toanother time definition, for example, a time interval between two clocksignals; and

ii. the detector pixel location with respect to a coordinate system, atthe time of the impinging.

The knowledge of time and location enables the determination ofcoincidence counts, namely photon counts that arrive substantiallysimultaneously, 180 degrees apart.

The time and location data may be stamped onto the radiation-event datapacket, for example, as a header or as a footer, or otherwise associatedwith the radiation-event data packet, as known.

The time-stamped data available in PET studies may further be used forperfusion studies, where the timing of physiological processes of shortdurations, that is, durations shorter than about half the time spanbetween heartbeats, is important. Perfusion studies usually involve asequence of continuous acquisitions, each of which may represent dataacquisition duration of about 10-30 seconds, although longer durationsare sometimes employed. Data from each of the frames is independentlyreconstructed to form a set of images which can be visualized and usedto estimate physiological parameters. This approach involves selectionof the set of acquisition times, where one must choose betweencollecting longer scans with good counting statistics but poor temporalresolution, or shorter scans that are noisy but preserve temporalresolution.

US Patent Application 2003010539, to Tumer, et al., published on Jun. 5,2003, and entitled, “X-ray and gamma ray detector readout system,”describes a readout electronics scheme, under development for highresolution, compact PET (positron emission tomography) imagers, usingtime tagging, based on LSO (lutetium ortho-oxysilicate,Lu.sub.2SiO.sub.5) scintillator and avalanche photodiode (APD) arrays.

There is some work relating to timing data in SPECT systems, employingAnger cameras.

U.S. Pat. No. 5,722,405, to Goldberg, issued on Mar. 3, 1998, andentitled, “Method and apparatus for acquisition and processing of eventdata in semi list mode,” describes a system for acquisition, processingand display of gated SPECT imaging data for use in diagnosing CoronaryArtery Disease (CAD) in nuclear medicine, employing an Anger camera, andprovides a physician with two parameters for evaluating CAD: informationrelating to the distribution of blood flow within the myocardium(perfusion) and information relating to myocardium wall motion(function). One aspect provides the physician with a display offunctional images representing quantitative information relating to bothperfusion and function with respect to selected regions of interest ofthe subject heart at end-diastole and end-systole segments of thecardiac cycle. The functional display consists of arcs of varied widthdepending on wall motion and color coded to illustrate degrees ofmyocardial perfusion for different pie shaped sections of a selectedregion of interest within a given short axis slice of reconstructedvolume data. Another aspect provides a series of display images allowingfacilitated access, display, and comparison of the numerous image framesof the heart that may be collected during gated SPECT sessions. U.S.Pat. No. 5,722,405 also teaches the ability to define and recallparameter files representative of data acquisition and processingparameters and protocol for use in gated SPECT studies and includes asemi-list processing mode to increase efficiency of data acquisitionwithin a camera computer system.

U.S. Pat. No. 7,026,623, to Oaknin, et al., issued on Apr. 11, 2006, andentitled, “Efficient single photon emission imaging,” describes a methodof diagnostic imaging in a shortened acquisition time for obtaining areconstructed diagnostic image of a portion of a body of a human patientwho was administered with dosage of radiopharmaceutical substanceradiating gamma rays, using SPECT and an Anger camera. The methodcomprises acquiring photons emitted from said portion of the body, bymeans of a detector capable of converting the photons into electricsignals, wherein the total time of photon acquiring is substantiallyshorter than the clinically acceptable acquisition time; processing saidelectric signals by a position logic circuitry and thereby deriving dataindicative of positions on said photon detector crystal, where thephotons have impinged the detector; and reconstructing an image of aspatial distribution of the pharmaceutical substance within the portionof the body by iteratively processing said data. For example, the methodincludes effective acquisition time of less than 10 minutes, or lessthan 8 minutes, and acquiring photons in a list-mode procedure.

SUMMARY OF THE INVENTION

The present invention relates to a dynamic SPECT camera, whichcomprises, a plurality of single-pixel detectors, a timing mechanism, incommunication with each single-pixel detector, configured for enablingtime-binning of the radioactive emissions impinging upon eachsingle-pixel detector to time periods not greater than substantially 30seconds, and a position-tracker, configured for providing information onthe position and orientation of each single-pixel detector, with respectto the overall structure, substantially at all times, during theindividual motion, the dynamic SPECT camera being configured foracquiring a tomographic reconstruction image of a region of interest ofabout 15×15×15 cubic centimeters, during an acquisition time of 30seconds, at a spatial resolution of at least 10×10×10 cubic millimeter.The dynamic camera is further configured for very short damping time,when in stop and shoot acquisition mode and may further acquire imagesin a stationary mode, with no motion. It is further configured for timebinning at dynamically varying time-bin lengths, dynamically determininga spectral energy bin for each single-pixel detector, and constructingand employing an anatomic system of voxels in the imaging andreconstruction.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. In case of conflict, the patentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

Implementation of the method and system of the present inventioninvolves performing or completing selected tasks or steps manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of preferred embodiments of the method andsystem of the present invention, several selected steps could beimplemented by hardware or by software on any operating system of anyfirmware or a combination thereof. For example, as hardware, selectedsteps of the invention could be implemented as a chip or a circuit. Assoftware, selected steps of the invention could be implemented as aplurality of software instructions being executed by a computer usingany suitable operating system. In any case, selected steps of the methodand system of the invention could be described as being performed by adata processor, such as a computing platform for executing a pluralityof instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the drawings:

FIGS. 1A-1D schematically illustrate a dynamic SPECT camera, inaccordance with embodiments of the present invention;

FIGS. 2A and 2B schematically illustrate the camera structure with theassemblies, in accordance with an embodiment of the present invention.

FIGS. 3A-3D schematically illustrate viewing positions, in accordancewith embodiments of the present invention.

FIGS. 4A-4F schematically illustrate stereo views and cross views, inaccordance with embodiments of the present invention.

FIGS. 5A and 5B illustrate experimental radiopharmaceutical data, asknown;

FIGS. 5C-5F illustrate cardiac gating, in accordance with embodiments ofthe present invention;

FIG. 6A-6I illustrate an intracorporeal dynamic SPECT camera, inaccordance with embodiments of the present invention;

FIG. 7 illustrates assembly damping parameters, in accordance withembodiments of the present invention;

FIGS. 8A and 8B schematically illustrate grid and anatomicalconstructions of voxels, in accordance with embodiments of the presentinvention;

FIGS. 9A-9J present experimental data, obtained by the dynamic SPECTcamera, in accordance with embodiments of the present invention;

FIG. 10 presents experimental data, obtained by the dynamic SPECTcamera, in accordance with embodiments of the present invention;

FIG. 11 illustrates components of the dynamic SPECT camera, inaccordance with embodiments of the present invention; and

FIG. 12 illustrates an electrical scheme, in accordance with embodimentsof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a dynamic SPECT camera, whichcomprises, a plurality of single-pixel detectors, a timing mechanism, incommunication with each single-pixel detector, configured for enablingtime-binning of the radioactive emissions impinging upon eachsingle-pixel detector to time periods not greater than substantially 30seconds, and a position-tracker, configured for providing information onthe position and orientation of each single-pixel detector, with respectto the overall structure, substantially at all times, during theindividual motion, the dynamic SPECT camera being configured foracquiring a tomographic reconstruction image of a region of interest ofabout 15×15×15 cubic centimeters, during an acquisition time of 30seconds, at a spatial resolution of at least 10×10×10 cubic millimeter.The dynamic camera is further configured for very short damping time,when in stop and shoot acquisition mode and may further acquire imagesin a stationary mode, with no motion. It is further configured for timebinning at dynamically varying time-bin lengths, dynamically determininga spectral energy bin for each single-pixel detector, and constructingand employing an anatomic system of voxels in the imaging andreconstruction.

The principles and operation of the dynamic SPECT camera according toaspects of the present invention may be better understood with referenceto the drawings and accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

Dynamic SPECT Camera

Design Description of the Dynamic SPECT Camera

An aspect of the present invention relates to a dynamic SPECT camera,with temporal and spatial resolutions which meet, even outperform thoseof PET, and with a high spectral resolution not available in PET.

Temporal resolution, as used herein, relates to a minimal acquisitiontime for a tomographic reconstruction image of a predetermined volume,for example 15×15×15 cubic centimeters, and predetermined spatialresolution, for example, 10×10×10 cubic millimeters. The minimalacquisition time may be, for example, 30 seconds, 10 seconds, or 1second.

Reference is now made to FIGS. 1A-1D, which schematically illustrate adynamic SPECT camera 10, in accordance with embodiments of the presentinvention. The dynamic SPECT camera 10 comprises:

an overall structure 15, which defines proximal and distal ends and,with respect to a body 100;

a first plurality of assemblies 20, for example, 6, 9, or 16 assemblies20, arranged on the overall structure 15, forming an array 25 of theassemblies 20, each assembly 20 comprising:

-   -   a second plurality of detecting units 12, each detecting unit 12        including:        -   a single-pixel detector 14, for detecting radioactive            emissions; and        -   a dedicated collimator 16, attached to the single-pixel            detector 14, at the proximal end thereof, for defining a            solid collection angle δ for the detecting unit 12.

Additionally, each assembly 20 comprises an assembly motion provider 40,configured for providing the assembly 20 with individual assemblymotion, with respect to the overall structure 15, during the acquisitionof radioactive-emission data for a tomographic image.

The dynamic SPECT camera 10 further includes:

-   -   a timing mechanism 30, in communication with each single-pixel        detector 14, configured for enabling time-binning of the        radioactive emissions impinging upon each single-pixel detector        14 to time periods not greater than substantially 30 seconds;        and    -   a position tracker 50, configured for providing information on        the position and orientation of each detecting unit 12, with        respect to the overall structure 15, substantially at all times,        during the individual assembly motion.

The dynamic SPECT camera 10 is configured for acquiring a tomographicreconstruction image of a region of interest of about 15×15×15 cubiccentimeters, for example, of a target organ 110, such as a heart or astomach, during an acquisition period no greater than 300 seconds, at aspatial resolution of at least 10×10×10 cubic millimeters.

It will be appreciated that the time period may be no greater than 200seconds, 100 seconds, 60 seconds, 30 seconds, 10 seconds, or 1 second.

Additionally, the dynamic SPECT camera 10 is configured for acquiring aseries of tomographic reconstruction images of a region of interest, asa function of time, at a rate of at least a tomographic reconstructionimage every 300 seconds.

Again, the rate may further be every 200 seconds, 100 seconds, 60seconds, 30 seconds, 10 seconds, or 1 second.

In accordance with embodiments of the present invention, the individualassembly motion may be, for example, an assembly oscillatory sweepingmotion, as described by an arrow 60. Additionally or alternatively, theindividual assembly motion may be a first oscillatory lateral motion, asdescribed by an arrow 80. Additionally or alternatively, the individualassembly motion may be a second oscillatory lateral motion, orthogonalto the first, as described by an arrow 90. Thus, the assembly motionprovider 40 may comprise between one and three motion providing units,for the different assembly motions.

Alternatively, the individual assembly motion is an assembly oscillatorysweeping motion, as described by an arrow 60, while the array 25 moveswith either the first or the second oscillatory lateral motions,described by the arrows 80 and 90, or with both.

Additionally, the detecting units 12 may be grouped into square orrectangular blocks 18, for example, of 4×4 detecting units 12, as seenin FIG. 1A, or of 16×16, 64×64, 64×128 or another number of detectingunits 12. Furthermore, the blocks 18 may be provided with individualblock oscillatory sweeping motion, as described by an arrow 70, withrespect to the overall structure 15, during the acquisition ofradioactive-emission data for a tomographic image. Preferably, the blockoscillatory sweeping motion is orthogonal to, or at an angle to theassembly oscillatory sweeping motion, described by the arrow 60. Thus,the assembly motion provider 40 may further comprise a dedicated blockmotion providing unit, in communication with each block of an assembly.

A control unit 55 may be integrated with the dynamic SPECT camera 10, soas to form a single physical unit, or in communication with the dynamicSPECT camera 10.

A spectral selection mechanism 56, in communication with each of thedetecting unit 12, is discussed hereinbelow, under the heading,“dynamically varying spectral bins.”

The body 100 may be a human or an animal, and the region of interest, orthe target organ 110 may be a heart, a brain, a breast, a stomach, a GItract, a colon, a prostate, a uterus, a cervix, a vagina, a throat, agland, a lymph node, a portion of skin, a portion of bone, portion ofanother tissue, or another body portion.

As seen in FIGS. 1A and 1B, a reference x;y;z coordinate systemillustrates a preferred orientation of the dynamic SPECT camera 10 withrespect to the body 100, wherein z runs along a length of the body 100.For convenience, the assembly axis along the assembly length will bereferred to as the assembly longitudinal axis, and the assembly axisalong the assembly width will be referred to as the assembly traverseaxis.

Preferably, the assemblies 20 are long and narrow columns, arrangedlongitudinally against the body 100, wherein the oscillatory sweepingmotion, described by an arrow 60, is about the z-axis. It will beappreciated that other arrangements are similarly possible.

As seen in FIG. 1C, illustrating a cross-sectional view in the x-yplane, preferably, the assemblies 20 are arranged in an arc or anarc-like structure, about the body 100, maintaining a shape that followsthe body contours, so as to keep as close as possible to the body 100.

FIG. 1D provides details of the detecting unit 12. The collimator has alength L, a collection angle δ, and a septa thickness τ. The singlepixel detector is preferably a square of sides D and a detectorthickness τ_(d).

Preferred dimensions for the detecting unit 12 may be, for example, 2.46mm×2.46 mm, and the solid collection angle δ may be at least 0.005steradians. Generally, there may be 16×64 detecting units 12 per block18.

The detector 14 is preferably, a room temperature, solid-state CdZnTe(CZT) detector, which is among the more promising that is currentlyavailable. It may be obtained, for example, IMARAD IMAGING SYSTEMS LTD.,of Rehovot, ISRAEL, 76124, www.imarad.com, or from eV Products, adivision of II-VI Corporation, Saxonburg Pa., 16056, or from or fromanother source. Alternatively, another solid-state detector such asCdTe, HgI, Si, Ge, or the like, or a combination of a scintillationdetector (such as NaI(Tl), LSO, GSO, CsI, CaF, or the like) and aphotomultiplier, or another detector as known, may be used, preferablywith a photomultiplier tube for each single-pixel detector 14 andcollimator 16, for accurate spatial resolution.

Reference is further made to FIGS. 2A and 2B which schematicallyillustrate the structure 15 with the assemblies 20, in accordance withan embodiment of the present invention. As seen, the assemblies 20 arearranged in an arc of an angle α, around the body 100, and move in theassembly oscillatory sweeping motion, about the z-axis, so as to providea plurality of views of the heart 110, from many positions, along thex-y plane.

As seen in FIGS. 2A and 2B, the dynamic camera 10 is configured forsimultaneous acquisition by the assemblies 20, each scanning the sameregion of interest from a different viewing position, thus achievingboth shorter acquisition time and better edge definitions.

Preferably, the structure 15 conforms to the contours of the body 100,so as to maintain substantial contact or near contact with the body.

The embodiment of FIGS. 2A and 2B illustrate a single type ofmotion-assembly oscillatory sweeping motion about the z-axis, asdescribed by the arrow 60 (FIG. 1A). In some cases, additional motionsor views from additional directions may be desirous, as illustrated inFIGS. 3A-3D, hereinbelow.

Reference is further made to FIGS. 3A-3D, which schematically illustrateviewing positions, in accordance with embodiments of the presentinvention.

FIG. 3A illustrates a cylindrical target organ 110, with a cylindricalradioactive emission source 115 therein.

As seen in FIG. 3B, a view along the x-axis will observe the cylindricalradioactive emission source 115 as a bar 115.

As seen in FIG. 3C, a view along the y-axis will similarly observe thecylindrical radioactive emission source 115 as a bar 115, thus notadding new information to the view along the x axis.

It will be appreciated that in the present example, any view along thex-y plane will observe the radioactive emission source 115 as a bar 115.

As seen in FIG. 3D, a view along the z-axis will observe the cylindricalradioactive emission source 115 as a circle 115, adding new informationto the views along the x and y axes.

As FIGS. 3A-3D illustrate, at times, views along two axes may beinsufficient for a three-dimensional definition of an object, and it maybe beneficial to include views with a component along the third axis.For the sake of definition, views along two axis will be referred tostereo views, while views that include a component of the third axiswill be referred to as cross views, since they intersect the planerstereo views.

Reference is further made to FIGS. 4A-4F, which schematically illustratestereo views and cross views, in accordance with embodiments of thepresent invention.

FIG. 4A illustrate the body 100 with a single assembly 20 arranged forviewing, for example, the heart 110. The assembly 20 is afforded withassembly oscillatory sweeping motion along the z-axis, as described bythe arrow 60, and preferably also first and second preferably orthogonaloscillatory lateral motions, described the arrows 80 and 90,respectively.

As seen in FIG. 4B, the assembly oscillatory sweeping motion along thez-axis, described by the arrow 60, produces views 65 in the x-y planes.The first and second orthogonal oscillatory lateral motions, describedthe arrows 80 and 90, augment these with additional views 65 in the x-yplanes. The purpose of the first and second oscillatory lateral motionsis to compensate for “dead areas,” that is, structural areas and otherareas that do not participate in the detection, within the assembly 20and between the assemblies 20, so as to provide complete coverage of thebody 100, by the array 25 (FIG. 1A). These motions produce viewssubstantially in the x-y plane. It will be appreciated that there is acomponent of viewing in a third axis, due to the solid collection angleof the collimator 16. Yet this component is rather small.

Returning to FIG. 4A, the blocks 18 of the assembly 20 may be furtherafforded with block oscillatory sweeping motion, described by the arrow70 and preferably orthogonal to the assembly oscillatory sweeping motiondescribed by the arrow 60.

As seen in FIG. 4C, the block oscillatory sweeping motion, described bythe arrow 70, produces cross views 75, which supplement views 65, byproviding components of the third axis, namely, the z axis. Asillustrated in FIGS. 3A-3D, hereinabove, the views 75 may add additionalinformation, not available or barely available in the views 65 along thex-y planes.

FIGS. 4D and 4F illustrate an alternative mode for acquiring the crossviews 75. Accordingly, the dynamic camera 10 further includes assemblies22, arranged at an angle β to the assemblies 20, and moving with anassembly oscillatory sweeping motion, described by an arrow 62, so as toprovide the cross views 75.

The Position Tracker 50

The position tracker 50 is configured for providing information on theposition and orientation of each detecting unit 12, with respect to theoverall structure 15, substantially at all times, during the individualassembly motion.

In accordance with a preferred embodiment of the present invention, theposition tracker 50 relates to software and (or) hardware that receiveinformation from the motion provider 40 and calculate the position andorientation of each detecting unit 12, based on that information.Preferably, the calculation is performed within the control unit 55.

Alternatively, position sensors, as known, may be used for determiningthe position and angular orientation of each detecting unit 12.

Alternatively still, a combination of information from the motionprovider 40 and position sensors may be employed.

The Timing Mechanism 30

The timing mechanism 30 associates timing information with theradioactive emission data impinging the single-pixel detectors 14 of thedetecting units 12. Preferably the timing mechanism 30 includes a singleclock used for all of the single-pixel detectors 14 in the dynamic SPECTcamera 10, so that timing information is synchronized for the camera asa whole. The timing information is collected at the single-pixel level,so that time-binning may be performed for the emission data collected byeach pixel. Exemplary methods for associating timing information withthe radioactive emission data include:

-   1) Time stamping—Each event, impinging on a given single-pixel    detector 14 at a given time is stamped with a time of detection and    a pixel identification. Stamping may be performed by any manner    known in the art, for example as a data packet header or footer. The    time-stamped, pixel stamped radioactive emission data may be binned,    per time and per pixel, by the control unit 55.-   2) Time binning—In an alternate approach, timing information is    provided for a cumulative count collected from each single-pixel    detector 14 over a fixed time interval, for example, 0.001 seconds,    1 second, or 10 seconds, rather than for individual events. Each    time bin is then stamped with a time stamp or sequential number and    a pixel identification. One technique for performing time binning,    is to insert a periodic clock pulse into the data stream. The    interval between the clock pulses equals the minimum bin length.    Thus, periodic pulses every 0.001 seconds may lead to bin lengths of    0.001 seconds or greater, for example, 1 second, or 10 seconds.    Time Scale Considerations

Dynamic studies, aimed at obtaining kinetic parameters, require theacquisition of full reconstructed images at a rate that is no greaterthan about half the frequency of the sampled kinetic parameter. Forexample, for adult humans, blood circulates through the body at a rateof about 1 cycle per minute. Thus, sampling a process affected by bloodcirculation should take place at a rate of at least two samplings perminute. Preferably, sampling should be at a much greater rate, forexample, 6 samplings or 10 samplings per minute—that is, about every 10seconds or about every 6 seconds.

Additionally, based on FIGS. 5A and 5B, according to Garcia et al. (Am.J. Cardiol. 51^(st) Annual Scientific Session, 2002), showingphysiological behavior of different radiopharmaceuticals, dynamicstudies for Tc-99m teboroxime are best performed within about the first100 seconds after administration, and better still, within the first 60seconds after administration.

Moreover, based on FIGS. 5A and 5B, the dynamic behavior of aradiopharmaceutical in the body, varies as a function of time, dependingon the radiopharmaceutical and on the time elapsed since itsadministration. For example, myocardial perfusion of Tc-99m teboroximeshows a very steep uptake between about the first 10-15 seconds and thefirst 50-60 seconds, followed by a more gradual washout, after the first60 seconds. The rate of sampling of Tc-99m teboroxime, during the first60 seconds after administration should be adjusted to the very steepuptake, for example, a sampling rate of every second. Forradiopharmaceutical with a slower dynamic behavior, a slower rate may besufficient.

It will be appreciated that a dynamic analysis requires preciseknowledge of the time of administration.

Obtaining the Time of Administration of a Radiopharmaceutical

As noted hereinabove, precise knowledge of the time of administration ofa radiopharmaceutical is important both in order to evaluatephysiological processes made visible by the radiopharmaceutical, withrespect to the time of the radiopharmaceutical's entry to the body andin order to perform the evaluation at an optimal period, with respect tothe radiopharmaceutical's cycle in the body.

There are several methods for acquiring precise knowledge of the time ofadministration of the radiopharmaceutical, as follows:

-   1. providing communication means between an administration device,    for example, a syringe or an IV device, and the dynamic SPECT camera    10, and communicating the precise time of administration, vis a vis    a clock, by the administration device to the dynamic SPECT camera    10. This method may be employed for example, when administration    takes place when the patient is positioned at the dynamic SPECT    camera 10, for imaging.-   2. providing communication means between the administration device,    the dynamic SPECT camera 10, and a third unit, for example, a    control system or a hospitals ERP system, communicating the precise    time of administration, vis a vis a clock, by the administration    device to the third unit, and reporting the precise time of    administration by the third unit to the dynamic SPECT camera 10.    This method may be employed for example, when administration takes    place at a different location than the imaging station.-   3. allowing the dynamic SPECT camera 10 to image the site of    administration, for example, the arm of the patient, while    administration takes place, while employing the timing mechanism 30    of the dynamic SPECT camera 10. A marker, for example, a line of    radioactive ink may drawn, for example, on the patient's arm or on    the administration device, for defining the time of administration    as the time the radiopharmaceutical first crosses the marker.    Alternatively, observing a flow of the radiopharmaceutical in the    administration device or in the patient's vein may be used to    determine the time of administration.-   4. Observing a transparent administration device, for example, with    a video camera, associated with a clock, may be employed for    defining a time of administration based on the radiopharmaceutical    distribution in the administration device, or based on the time the    radiopharmaceutical first crosses a marker, visible by the video    camera. Communication between the video camera and the dynamic SPECT    camera 10, or between the video camera, the dynamic SPECT camera 10,    and a third unit will provide the information to the dynamic SPECT    camera 10.

In accordance with embodiments of the present invention, theadministration may include various administration profiles, for example,bolus, continuous drip, or sinusoidal.

Cardiac Gating

The timing mechanism 30 of the dynamic SPECT camera 10 may further beemployed for cardiac gating, which is described in detail under acorresponding section, hereinbelow.

When cardiac gating is employed, time binning to time intervals nogreater than 50 milliseconds is employed.

Reference is now made to FIGS. 5C-5F, which illustrate cardiac gating inaccordance with the present invention.

In essence, two different approaches are presented for cardiac gating.In the first, the cardiac RR cycle is divided to a predetermined numberof graduations, for example, 16 or 32, so each is of somewhat differenttime span. In the second, a predetermined graduation time length ischosen, together with an alignment mark for aligning the graduationswith a specific state of the RR cycle, and a discard zone is provided,generally around the U-wave region, since the RR cycle may not beexactly divisible by the predetermined graduation time lengths. Thecardiac gating may be performed with respiratory gating.

Thus, in accordance with a first embodiment of the present invention,illustrated in FIG. 5C, a method of radioactive-emission imaging of aheart is provided, comprising:

imaging the heart of a body, for an imaging period greater than at least2 cardiac electrical RR cycles 81;

post processing for identifying an average RR interval, based on actualRR time intervals 82, for the body;

post processing for evaluating each specific cardiac electrical cycle,vis a vis the average RR interval, and identifying each of the specificcardiac electrical cycles 81, either as “good,” which is to be includedin the imaging, or as “bad,”, for example, due to Arrhythmias, whereinthe “bad” cycles are discarded;

dividing each of the “good” cardiac electrical cycles to a fixed numberof time graduations 83, for example, 16 or 32;

indexing each graduation 83 with cardiac-cycle indices 84, whichassociate each graduation with a cardiac-cycle time bin, based on itsrelative position in the cardiac cycle, for example, with respect to theP-wave, T-Wave, U-wave (see FIG. 5F), for example, by assigning a commonbin to each P-wave peak, and another common bin to each U-wave dip, andso on; and

adding up photon counts that occurred within the graduations of the samecardiac-cycle bin, from the different “good” RR cycles 81.

Additionally, the method may include performing ECG, concurrent with theimaging, and using the ECG input for identifying durations of the RRintervals 82.

In accordance with an additional embodiment, illustrated in FIG. 5D, themethod includes:

extending the imaging period to cover at least two respiratory cycles85;

dividing each of the respiratory cycles 85 to respiratory-cycle stagesand assigning each of the respiratory-cycle stages a respiratory-cycleindex, dividing it into bins, such as bins 86 or 87;

adding up photon counts that occurred within the graduations of commoncardiac-cycle and respiratory-cycle bins, such as cardiac-cycle index 96and respiratory index 86, or cardiac-cycle index 97 and respiratoryindex 87, so as to eliminate respiratory effects.

In accordance with an alternative embodiment, illustrated in FIG. 5C,the graduations 83 are fine graduations, and further including:

amalgamating the fine graduations 83 to coarse graduations 89, whereineach of the coarse graduation 89 includes at least two fine graduations83;

indexing each coarse graduation of each of the dedicated graduation timescales with cardiac-cycle indices 91 (analogous to the cycle 84); and

adding up photon counts that occurred within the coarse graduations 89of the same cardiac-cycle index bin, for the different “good” RR cycles.

In accordance with an embodiment of the present invention, for eachvoxel of a reconstructed image, adding up photon counts includes addingup photon counts which occurred within the graduations of the samecardiac-cycle index, for that voxel, from the plurality of detectingunits 12.

Alternatively, for each voxel of a reconstructed image, adding up photoncounts includes adding up photon counts which occurred within thegraduations of common cardiac-cycle and respiratory-cycle indices, forthat voxel, from the plurality of detecting units 12.

In accordance with another embodiment of the present invention,illustrated in FIG. 5E, a method of radioactive-emission imaging of aheart, comprises:

providing a fixed graduation time scale 92, with graduations 93 and atleast one graduation mark 94, operative as a point of alignment;

aligning the point of alignment with a specific stage of each of thecardiac electrical cycles, such as “Q,” or “R,” thus, in effectassigning each one of the cardiac electrical cycles 81 a dedicated oneof the graduation time scales 92; and

allowing for a discard zone 95, between adjacent ones of the dedicatedgraduation time scales 92, where necessary.

Furthermore, the method includes using the ECG input for the aligning ofthe point of alignment 94 with the specific stage of each of the cardiacelectrical cycles, such as “Q,” or “R.

It will be appreciated that when stop and shoot acquisition mode isused, the motion of the assemblies 20 is planned to take place duringspecific portions of the RR cycle.

Spatial and Temporal Resolution

In order to meet the time scale considerations, described hereinabove,the dynamic SPECT camera 10 according to embodiments of the presentinvention is designed at least for acquiring a tomographicreconstruction image of about 15×15×15 cubic centimeters, which isapproximately the volume of a heart, at a predetermined spatialresolution of at least 10×10×10 cubic millimeters, at an acquisitiontime no greater than about 30 seconds. Preferably, the acquisition timeis no greater than about 10 seconds, and more preferably, theacquisition time is no greater than about 1 second.

Additionally, the spatial resolution of the tomographic reconstructionimage may be at least 7×7×7 cubic millimeters, or better yet, at least4×4×4 cubic millimeters, or better still, at least 1×1×1 cubicmillimeters.

When cardiac gating is employed, time binning to time intervals nogreater than 50 milliseconds is employed.

Dynamically Varying Time-Bin Lengths

There are times when dynamically varying time-bin lengths are desired.For example, Tc-99m-teboroxime has an uptake curve (FIG. 5B) which isvery steep during the uptake and which becomes less so during thewashout. Thus, different time-bin lengths may be desired for differentportions of the Tc-99m-teboroxime uptake curve. Similarly, differentradiopharmaceuticals have different uptake curves, and dedicatedtime-bin lengths may be desired for each radiopharmaceuticals, and fordifferent portions of their respective uptake curves. Moreover, thecardiac RR cycle has very steep periods, during the rise and fall of theR peak (FIG. 5F), followed by periods that are nearly flat as a functionof time. Again, time bin lengths of different durations may be employedfor the different portions of the RR cycle. Furthermore, while theactual region of interest, for example, the heart, requires imaging at avery high level of accuracy, adjacent regions, for example, the chestmuscle, may be of lesser interest, and may be viewed at time bins ofgreater lengths. Additionally, continuous acquisition mode may requireshorter time-bin lengths than stop and shoot mode.

For example, the actual rise and fall of the R peak may be gated at timebins of 10 milliseconds, while the nearly leveled U-wave may be gated at100 milliseconds. Similarly, while the heart muscle may be gated at anaverage time bin of 50 milliseconds, the adjacent chest muscle may begated at time bins of 1 second and longer. It will be appreciated thatother values may similarly be employed.

In accordance with embodiments of the present invention, a lookup systemof recommended time-bin lengths may be provided, for specifyingrecommended time-bin lengths as functions of at least one of thefollowing:

a specific region of interest;

an administered radiopharmaceutical;

time elapsed since the administration of the radiopharmaceutical;

cardiac state with respect to an RR cycle;

a view of the detecting unit 12, with respect to the region of interest;

patient general data; and

data acquisition mode.

The lookup system may be, for example, tables or curves.

Thus the dynamic SPECT camera 10 may be configured for time binning atdynamically varying time-bin lengths, by providing communication betweenthe timing mechanism 30 and the lookup system, wherein the timingmechanism is configured for selecting a recommended time-bin length fromthe lookup system, for each time bin.

Dynamically Varying Spectral Bins

It is sometimes of value to image only a specific spectral bin so as toeliminate scatter or contributions from other radiopharmaceuticals.Additionally, it may be of value to image several spectral binssimultaneously, for different radiopharmaceuticals, wherein differentgroups of detecting units are dedicated to different spectral bins.

Thus, the dynamic SPECT camera 10 may be configured for dynamicallydetermining a spectral energy bin for each detecting unit 12, asfollows:

providing a spectral selection mechanism 56 (FIG. 1A), for enabling aselection of a spectral energy bin to be used for each detecting unit12, independently from the other detecting units 12; and

a lookup system of recommended spectral energy bin values, as functionsof at least one of a specific region of interest, an administeredradiopharmaceutical, time since the administration of theradiopharmaceutical, a view of the detecting unit with respect to theregion of interest, and patient's details;

wherein the spectral selection mechanism 56 is further configured fordynamically determining the spectral energy bin for each detecting unit,as functions of the specific region of interest, the administeredradiopharmaceutical, the time elapsed since the administration of theradiopharmaceutical, the view of the detecting unit with respect to theregion of interest, and patients' details, from the lookup system.

The spectral energy bin is designed to include a primary photon energy±10%, or the primary photon energy ±7%, or the primary photon energy±5%.

Additionally, at least two radiopharmaceuticals may be administered andviewed by different groups of detecting units, each group beingconfigured for a different spectral energy bin, so as to view eachradiopharmaceutical in the same region independently of the otherradiopharmaceutical.

The spectral selection mechanism may be a hardware unit or a software.

The spectral selection may be performed during data acquisition, orlater.

Intracorporeal dynamic SPECT Camera

Referring further to the drawings, FIGS. 6A-6I describe the dynamicSPECT camera 10 as an intracorporeal dynamic SPECT camera 10, whichincludes a single assembly 20, preferably configured for oscillatorysweeping motion around its longitudinal axis—the z axis, as described bythe arrow 60. The blocks 18 may be further configured for oscillatorysweeping motion in an orthogonal direction, as described by the arrows70. An end block 18′ may be further configured for motion, for example,as described by the arrow 70′. It will be appreciated that other motionsare similarly possible, for example, oscillatory lateral motions, orrotational motions. For example, the arrow 90 describes the oscillatorylateral motion along the z axis of the assembly 20.

An ultrasound transducer 45 may be included with the intracorporealdynamic SPECT camera 10.

Other features of the intracorporeal dynamic SPECT camera 10 are asdescribed for the dynamic SPECT camera 10 of FIGS. 1A-1D.

FIG. 6A illustrates the intracorporeal dynamic SPECT camera 10 as asingle rigid unit, for example, for rectal or vaginal insertion. FIG. 6Cillustrates the intracorporeal dynamic SPECT camera 10 as having anincorporeal portion 44, an extracorporeal portion 42 and a cable 46, forexample, for insertion to the esophagus.

FIGS. 6F and 6E illustrate motions of the blocks 18, as described by thearrows 70. FIGS. 6F-6I illustrate motion of the assembly 20, asdescribed by the arrow 60.

Image Acquisition Modes

In accordance with embodiments of the present invention, several imageacquisition modes are available, as follows:

In a continuous acquisition mode, also referred to as fanning, data isacquired while the array, assembly, or block are in continuous motion.Continuous acquisition mode may apply also to oscillatory motions,although strictly speaking there is a momentary pause with each changeof direction. This mode leads to some blurring of the data, but it doesnot require the array, assembly, or block to stabilize between periodsof motion and periods of stationary data acquisition.

In a stop and shoot acquisition mode, incremental travels are followedby stationary acquisition intervals. This mode leads to betterresolution, yet it requires a damping period, to allow the array,assembly, or block to stabilize between periods of motion and periods ofstationary data acquisition, as discussed hereinbelow, under theheading, “Stability and Damping Time”.

Interlacing is a fast stop and shoot acquisition mode with oscillatorymotion, for example, sweeping oscillatory motion, wherein on rather thanstopping at each predetermined locations, with each sweep, the oddlocations are visited on a right sweep and the even locations arevisited on the left sweep, or vice vera, so that each sweeping directionstops at different locations.

Prescanning relates to a fast prescan of a subject undergoing diagnosis,to identify a region-of-interest, and thereafter collect higher qualitydata from the region-of-interest. A prescan according to the presentinvention may be performed by the dynamic SPECT camera 10, preferably,with interlacing, or in a continuous mode, or by any other imagingdevice, including, for example, ultrasound or MRI.

Stability and Damping Time

Stop and shoot acquisition mode involves discontinuities in motionbetween travel and shooting modes, and at the beginning of each shootingmode, the assemblies 20 must be allowed to stabilize till vibrations areless than about ±0.25 mm, so as not to interfere with the acquisition.

Prior art SPECT cameras must allow for a damping time of about 5seconds, but the dynamic SPECT camera 10, according to embodiments ofthe present invention reaches stability in about 1 second or less.

FIG. 7 schematically illustrate the assembly 20, according toembodiments of the present invention. The damping time for the assembly20 may be described as:Damping Time=CX[( 1/12)M(T ² +W ²)+MX ₀ ²],wherein:

M is the mass of the assembly 20;

T is the thickness of the assembly 20;

W is the width of the assembly 20;

X₀ is the axis of rotation; and

C is a constant that depends on the braking force applied to theassembly 20.

The factor 1/12 is calculated assuming the assembly proximal end istangential to the sweeping path.

As the damping time equation illustrates, the damping time is highlydependent on both the axis of rotation X₀ and the mass of the assembly20.

In the present case, the axis of rotation is that of the sweeping motiondescribed by the arrow 60 (FIG. 1A), which is considerably shorter thanan axis of rotation around the body 100.

Similarly, the mass of a single assembly is far less than that of aconventional SPECT camera.

Possible values for the assembly 20, according to embodiments of thepresent invention may be:

Weight of the assembly 20≈1.5 kg.

Thickness of the assembly 20≈5 cm.

Width of the assembly 20≈7 cm.

As such, the assembly is designed with a damping time constant of under50 msec during which vibrations amplitude subsides to under 0.25 mm.

It will be appreciated that the present example applies to bothextracorporeal and intracorporeal dynamic cameras.

Stationary Dynamic SPECT Camera

It may be desired to perform imaging, especially prescanning with astationary camera, that is without motion, for the following reasons:

1. in continuous acquisition mode, the blurring produced by the motionis eliminated;

2. in stop and shoot acquisition mode, the time spent in motion isavoided, as are the vibrations, associated with the discontinuitiesbetween the motions and the stationary intervals.

In general, a stationary camera does not provide sufficient viewingpositions and detecting units, yet the camera may be specificallydesigned to provide those, to a desired level.

Preferably, the assemblies 20 are positioned at optimal positions priorto imaging, and imaging takes place while the camera is stationary.

Thus, in accordance with embodiments of the present invention, there isprovided a stationary dynamic SPECT camera 10, which is described hereinwith reference to FIGS. 1A-1D. The stationary dynamic SPECT camera 10comprises:

the overall structure 15, which defines proximal and distal ends withrespect to a body;

the first plurality of the assemblies 20, arranged on the overallstructure 15, forming an array 25 of the assemblies 20, each assembly 20comprising:

-   -   a second plurality of detecting units 12, each detecting unit 12        including:        -   a single-pixel detector 14, for detecting radioactive            emissions; and        -   a dedicated collimator 16, attached to the single-pixel            detector, at the proximal end thereof, for defining a solid            collection angle δ for the detecting unit; and    -   an assembly motion provider 40, configured for providing the        assembly 20 with individual assembly motion with respect to the        overall structure, prior to the acquisition of        radioactive-emission data;

a position-tracker 50, configured for providing information on theposition and orientation of each of the detecting units 12, with respectto the overall structure 15, during the individual motion,

the stationary dynamic SPECT camera 10 being configured for acquiring atomographic reconstruction image of a region of interest whilestationary, for the whole duration of the tomographic image acquisition.

Preferably, the region of interest is about 15×15×15 cubic centimeters,and the tomographic image may be acquired during an acquisition time of60 seconds, at a spatial resolution of at least 20×20×20 cubicmillimeter.

Additionally, the tomographic image may be acquired during anacquisition time of 30 seconds, at a spatial resolution of at least20×20×20 cubic millimeter.

Furthermore, the tomographic image may be acquired during an acquisitiontime of 60 seconds, at a spatial resolution of at least 10×10×10 cubicmillimeter.

Additionally, the tomographic image may be acquired during anacquisition time of 30 seconds, at a spatial resolution of at least10×10×10 cubic millimeter.

Preferably, the structure 15 conforms to the contours of the body 100,for acquisition with substantial contact or near contact with the body.

Additionally, the assemblies 20 in the array 25 are configured toprovide stereo views in a plane and cross views.

Anatomic Construction of Voxels

Anatomic construction of voxels avoids the smearing effect of a rigidvoxel grid construction, where different tissue types, for example,blood and muscle, appear in a same voxel. This is important especiallyfor perfusion studies, where the perfusion of blood into the tissue issought.

Reference is now made to FIGS. 8A and 8B, which schematically illustratea rigid voxel grid construction and an anatomic construction of voxels,respectively, in accordance with the present invention.

FIGS. 8A and 8B illustrate a heart 200, having atria 202 and 204,chambers 206 and 208, and a muscle 218.

As seen in FIG. 8A, a rigid voxel construction 202 causes smearing ofthe different tissue types. However, as seen in FIG. 8B, blood andmuscle tissues are anatomically divided into different voxels, allowingan accurate study of perfusion. The atria and chambers are divided intoan anatomic voxel system 222, or to an anatomic voxel system 224, whilethe muscle is divided into a relatively coarse voxel system 226, or to afiner voxel system 228, as desired. It will be appreciated that theanatomic voxels may vary in volume. For example, since ischemia is notrelevant to the atria and chambers, they may be divided into coarsevoxels, while the heart muscle may be divided into fine voxels.

As further seen in FIG. 8B, the rigid voxel construction 202 may stillapplied to the surrounding chest muscle.

It will be appreciated that parametric equations, such as F(1) and F(2)may be created and used in the construction of the anatomic constructionof the voxels.

The following describes methods for obtaining the anatomic constructionof voxels.

A first method for the anatomic construction of voxels includes:

providing a structural image of a region of interest, such as a heart;

constructing an anatomic system of voxels, for the region of interest,in which voxel boundaries are aligned with boundaries of structuralobjects of the region of interest, based on the structural image;

performing radioactive-emission imaging of the region of interest,utilizing the anatomic system of voxels; and

performing reconstruction of the radioactive-emission imaging, utilizingthe anatomic system of voxels.

Preferably, the structural image is provided by a structural imager,selected from the group consisting of 2-D ultrasound, 3-D ultrasound,planner x-rays, CT x-rays, and MRI.

Additionally, the structural imager is co-registered to aradioactive-emission imaging camera which performs theradioactive-emission imaging.

Moreover, attenuation correction of the radioactive-emission imaging maybe performed, based on the structural image.

Furthermore, the structural image and the radioactive-emission image,constructed with the anatomic voxels, may be displayed together.

Alternatively, the structural imager is not co-registered to aradioactive-emission imaging camera which performs theradioactive-emission imaging, and further including corrections formisregistration.

Alternatively still, the structural image is provided from a lookupsystem, which is preferably corrected for patient's details.

It will be appreciated that the anatomic construction of voxels may bebased on fitting the boundaries of the structural objects to parametricequations and utilizing the parametric equations in the constructing ofthe anatomic system of voxels.

Additionally, the anatomic system of voxels includes voxels of varyingvolumes, depending on their anatomic position and relevance.

Furthermore, the method includes time-binning of the radioactiveemissions to time periods not greater than substantially 30 seconds, ornot greater than substantially 10 seconds, or not greater thansubstantially 1 second.

Additionally, the anatomic system of voxels includes voxels of varyingvolumes, depending on the relevance of their dynamic activity.

An alternative method for the anatomic construction of voxels includes,relates to the use of the radioactive emission imaging itself for theanatomic reconstruction, as follows:

providing a first system of voxels for a region of interest;

obtaining radioactive-emission data from the region of interest;

performing a first reconstruction, based on the radioactive-emissiondata and the first system of voxels, to obtain a first image;

correcting the first system of voxels, by aligning voxel boundaries withobject boundaries, based on the first image; thus obtaining a secondsystem of voxels;

performing a second reconstruction, based on the radioactive-emissiondata and the second system of voxels, thus obtaining a second image.

Alternatively, a set of radioactive emission data is obtained, possiblywith a second injection, in order to concentrate the viewing on theanatomic voxels, as follows:

providing a first system of voxels for a region of interest;

obtaining a first set of radioactive-emission data from the region ofinterest;

performing a first reconstruction, based on the first set of theradioactive-emission data and the first system of voxels, to obtain afirst image;

correcting the first system of voxels, by aligning voxel boundaries withobject boundaries, based on the first image; thus obtaining a secondsystem of voxels, which is anatomically based;

obtaining a second set of radioactive-emission data from the region ofinterest, based on the second system of voxels, which is anatomicallybased; and

performing a second reconstruction, based on the second set of theradioactive-emission data and the second system of voxels, thusobtaining a second image.

Anatomic Modeling

Bull's Eye, or polar map, is a semi-automatic method for thequantification and evaluation of coronary artery disease from SPECTtomograms obtained by marking the myocardium with Tl-201 or MIBI-Tc-99.The polar map is computed from cross-sectional slices of the LeftVentricle (LV). For each slice, the center and a radius of search thatcontains the LV are determined and the LV is divided into radialsectors. The maximum count value of each sector is computed, generatinga profile. Profiles are plotted as concentric circle onto the map. Theresulting map is a compression of 3D information (LV perfusion) onto asingle 2D image.

Yet the bull's eye or polar map is reconstructed from a rigorousgeometry of voxels, for example, of 5×5×5 mm, or 4×4×4 mm, which cutsacross tissue types, thus providing smeared information.

A voxel division that is based on an anatomical structure would behighly preferred, as it would allow the measurements of processes withinand across anatomical features, substantially without the smearingeffect. For example, if specific voxels are used to define bloodregions, and others are used to define muscle regions, than diffusionacross boundary membranes and other processes may be evaluated,substantially without a smearing effect.

Anatomical model is based on voxels that follow anatomical structures,and may be shaped for example, as a sphere, a tube, or as a shellsegment, rather than as a the standard cube.

When combined with a camera of high resolution and sensitivity and withgated measurements, anatomic modeling would be clearly advantageous overstandard, rigorous modeling, especially for kinetic studies aremeaningful only with respect to specific tissue types.

In accordance with embodiments of the present invention, the polar mapmay be produced with a reduced number of amplitudes, or levels, forexample, 7 levels of severity, or 5 levels of severity, from healthy tosevere.

Kinetic Modeling

As part of the imaging and analysis processes, the camera may be able toproduce a time series of 2D or 3D images, showing reconstructedintensity in space and its changes over time.

Likewise, it may be desirable not to reconstruct the entire volume butonly limited segments of interest. In those segments, resolution ofsegment definition may be very important in order to minimize partialvolume effect, which results in a biased estimate of the kineticprocess.

In an exemplary embodiment, the analysis of the kinetic process may beafter reconstruction of the intensity in the entire volume or in theselected segments has been done for a series of time points. In thatcase, each segment or location in space (u) has a list of intensity (I)values in time (t), and the list I(u,t) may be further analyzed to fitparametric kinetic model.

Such a parametric kinetic model may be a variety of kinds, depending onthe modeling on the biological process. Examples of such models may befound in PCT/IL2005/001173.

In a simplistic example, the model may beI(u,t)=B(t)·(1−e ^(−k) ¹ ^((u)·t))·e ^(−k) ² ^((u)·t)

where B(t) is a concentration in the blood, whether obtained fromimaging a segment which is pure blood (e.g. major blood vessel, orvolume within the heart chamber), or may be known from other sources (byinjection profile, other invasive or non invasive measurements from theblood, etc). k₁(u) is the time constant representing a process of uptakeinto the tissue at segment u, and k₂(u) is the time constantrepresenting a process of washout from the tissue at segment u.

There may be many other models, and for example the equation above maytake other forms such asI(u,t)=B(t)*F ₁(k ₁(u),τ)*F ₂(k ₂(u),τ)

where * stands for either multiply operation or convolution in mostcases, and F₁ and F₂ represent processes. In an example, the effect ofsuch process on the intensity may be modeled in linear cases byconvolution of the intensity in the blood with an impulse response of alinear process F₁(k_(i)(u),τ). Each of these may include one or moretime constants k_(i)(u), and the time profile is described as a functionof time τ. There may be one or more such processes F_(i), for example 1(e.g. uptake or decay only), 2 (e.g. simultaneous uptake and clearanceprocesses, 3 (e.g. combination with accumulation or metabolism), 4 ormore.

A process of fitting may be used between the reconstructed intensity inspace and time and the parametric models mentioned above.

In another example, the parametric model may be incorporated into thereconstruction process. In this case, it is not necessary to performreconstruction of intensities I(u,t) in space and time and then use thatinformation to extract time constants of biological processes k_(i)(u).

Instead, the imaging equation

$\left. {y_{n}(t)} \right.\sim{{Poisson}\left( \left\lbrack {\sum\limits_{u}{{\varphi_{n}(u)}{I\left( {u,t} \right)}}} \right\rbrack \right)}$

may be explicitly replaced with the model of the intensities

$\left. {y_{n}(t)} \right.\sim{{Poisson}\left( \left\lbrack {\sum\limits_{u}{{\varphi_{n}(u)}{B(t)}*{F_{1}\left( {{k_{1}(u)},\tau} \right)}*{F_{2}\left( {{k_{2}(u)},\tau} \right)}}} \right\rbrack \right)}$

(where y_(n)(t) is the number of photon measured from a viewing positionn with a probability function of the view φ_(n)(u)).

In this case, the reconstruction process (e.g. by Maximum-Likelihood,Expectation maximization, or other equation solving techniques) is usedto recover the best fitting values of k_(i)(u), instead of recoveringI(u,t) and then k_(i)(u).

In some embodiments of the present invention, the use of a cameradirectly intended to perform dynamic studies, the ability to avoidinterim recovery of intensities in 3D-space in various time periods maybe a benefit, as the design of the scanning is optimized for the kineticparameters reconstruction, and not necessarily to image quality in eachtime point.

Active Vision

The camera of the present invention may further include active visionwhich relates to a method of radioactive-emission measurements of a bodystructure, comprising:

performing radioactive-emission measurements of the body structure, at apredetermined set of views;

analyzing the radioactive-emission measurements; and

dynamically defining further views for measurements, based on theanalyzing.

Active vision may be used, for example, to better define an edge, bychanging a view direction, to direct a saturating detecting unit awayfrom a hot spot, to change the duration at a certain location, when agreater number of counts are required, or when sufficient counts havebeen obtained.

Reconstruction Stabilizer

The method of reconstruction employed by the present invention mayfurther include a method for stabilizing the reconstruction of an imagedvolume, comprising:

performing an analysis of the reliability of reconstruction of aradioactive-emission density distribution of said volume from radiationdetected over a specified set of views; and

defining modifications to at least one of a reconstruction process and adata collection process to improve said reliability of reconstruction,in accordance with said analysis.

Additionally, the method may include calculating a measure of saidreliability of reconstruction, said measure of reliability ofreconstruction being for determining a necessity of performing saidmodifications.

Furthermore, the method may include:

providing a detection probability matrix defining a respective detectionprobability distribution of said volume for each of said views;calculating the singular values of said detection probability matrix;

identifying singular values as destabilizing singular values.

Additionally, the method may include calculating a condition number ofsaid probability matrix as a measure of said reliability ofreconstruction.

It will be appreciated that this approach may result in non-uniformvoxels, wherein voxel volume may increase or decrease as necessary toincrease the reliability of the reconstruction

View Selection

The present invention further utilizes a method of optimal viewselection, as follows:

providing said volume to be imaged;

modeling said volume;

providing a collection of views of said model;

providing a scoring function, by which any set of at least one view fromsaid collection is scorable with a score that rates information obtainedfrom said volume by said set;

forming sets of views and scoring them, by said scoring function; and

selecting a set of views from said collection, based on said scoringfunction for imaging said volume.

Additionally, zooming in onto a suspected pathology may be performed bya two-step view selection, wherein once the suspected pathology isobserved, that region of the volume is modeled anew and a new collectionof views is obtained specifically for the suspected pathology.

Experimental Results

Reference is now made to FIGS. 9A-9J, which schematically illustratecardiac imaging of Tc-99m-Teboroxime, with the dynamic camera 10 inaccordance with aspects of the present invention. The significance ofthe experimental data provided herein is the ability to successfullyimage Teboroxime, which as FIG. 5B illustrates is washed out of the bodyvery quickly.

FIG. 9A provides anatomical landmarks, as follows:

-   -   Left Ventricle (LV)    -   Right Ventricle (RV)    -   Left Atrium (LA)    -   Right Atrium (RA)

FIG. 9B is a dynamic study input of bloodpool, mayocardium, and bodytimed activity.

FIG. 9C is a Film-stripe representation of a dynamic SPECT study, asfollows:

-   -   First 2 minutes after Tc99m-Teboroxime* injection, 10s/frame    -   Mid-ventricular slices (upper row:SA lower row:HLA)

Note: as the intense blood pool activity at the center of the heartchambers gradually clears, while the myocardial uptake graduallyintensifies.

FIG. 9D is a Film-stripe representation of a dynamic SPECT study, asfollows:

-   -   First 4 minutes after Tc99m-Teboroxime* injection, 10s/frame    -   Mid-ventricular slices (upper row:SA lower row:HLA)

Note: as the intense blood pool activity at the center of the heartchambers gradually clears, while the myocardial uptake graduallyintensifies

FIG. 9E is a Movie representation of a dynamic SPECT study (SA), asfollows:

-   -   First 4 minutes after Tc99m-Teboroxime* injection, 10s/frame    -   Mid-ventricular SA slices.

Note: as the intense blood pool activity gradually clears in LV and RVcavities

Note: Myocardial uptake gradually intensifies, (the thin walled RV isless intense)

FIG. 9F is a Movie representation of a dynamic SPECT study (SA), asfollows:

-   -   First 4 minutes after Tc99m-Teboroxime* injection, 10s/frame    -   Mid-ventricular SA slices.

Note: as the intense blood pool activity gradually clears in LV, RV, LAand RA cavities

Note: Myocardial uptake gradually intensifies, (the thin walled RV antatria are less intense)

FIG. 9G is a Movie representation of a dynamic SPECT study (fast).

FIG. 9H is a Movie representation of a dynamic SPECT study (slow).

FIG. 9I represents volume segmentation for separate tissue flow dynamicsmeasurement

FIG. 9J represents measured kinetic curves.

FIG. 10 is another experiment, illustrating time binning at a rate of0.001 seconds.

Electronic Scheme for Fast Throughput

High-sensitivity detecting units, such as the room temperature,solid-state CdZnTe (CZT) detectors utilized in the present embodiments,must be discharged frequently, as their high-sensitivity can lead torapid saturation. When a given detector saturates, the output count forthe associated pixel no longer accurately reflects the number ofincoming photons, but rather the maximum number that the detector iscapable of absorbing. This inaccuracy may lead to errors duringreconstruction. It is therefore important to perform readout oftenenough to avoid detector saturation.

The data channel from the assembly 20 (or the assembly 20 readoutcircuitry) to the signal processing components must be fast enough tohandle the large quantities of data which are obtained from thedetecting units 12.

The electronic scheme of the present embodiments preferably includes oneor more of the following solutions for performing frequent detector unitreadout, while maintaining high data throughput to prevent data channelsaturation.

In a preferred embodiment, the dynamic SPECT camera 10 includes aparallel readout unit for performing parallel readout of emission countdata. Parallel readout requires less time than serial readout (in whichthe pixels are read out in sequence), as multiple pixels may be read outin a single cycle without losing the information of the individual pixelcounts. The readout rate can thus be increased without loss of data.

Parallel readout may be performed at many levels. Reference is now madeto FIG. 11, which illustrates various levels of detector unitorganization at which parallel readout may be performed. The presentexemplary embodiment shows a single detector array 25, which includesthree assemblies 20. Each assembly includes a plurality of blocks 18 ofdetector units 12. Each detecting unit 12 includes a single-pixeldetector (FIG. 1D).

The parallel readout unit preferably performs parallel readout at thelevel of one or more of:

a) detecting units 12, each of the single-pixel detector 14;

b) blocks 18, which include a plurality of detecting units 12;

c) assemblies 20, which include a plurality of blocks 18

d) array 25, which includes a plurality of assemblies 20.

When the parallel readout unit performs parallel readout at the level ofthe detecting units 12, count values are read out in parallel from eachof the electrically insulated single-pixel detector 14. The single-pixeldetector 14 is discharged at readout, and the photon collection processbegins anew.

When the parallel readout unit performs parallel readout at the level ofthe block 18, count values from each of the detecting units 12 are readout serially, however multiple blocks 18 are read out in parallel. Thisapproach is less complex to implement than parallel readout of thedetecting units 12, although it results in a certain reduction inreadout rate to accommodate the serial readout. Again, the single-pixeldetectors 14 are discharged at readout.

Similarly, when the parallel readout unit performs parallel readout atthe level of the assembly 20, count values from each of the detectingunits 12 in the assembly 20 are read out serially, however multipleassemblies 20 are read out in parallel.

Parallel readout preferably includes multiple detection, amplificationand signal processing paths for each of the pixels, thereby avoidingsaturation due to a single localized high emission area—“hot spot”. Thisis in contrast with the Anger camera, in which multiple collimators areassociated with a single-pixel scintillation detector, and saturation ofthe scintillation detector may occur even due to a localized hot spot.

FIG. 12 illustrates an exemplary embodiment of parallel readout in thedynamic SPECT camera 10. Radioactive emissions are detected by pixelatedCZT crystals, where each crystal is divided into 256 pixels. The crystalis part of a ‘CZT MODULE’ (B) which also includes two ASICS eachreceiving events from 128 pixels. The ASIC is an OMS ‘XAIM3.4’ made byOrbotech Medical Systems, Rehovot, Israel, together with the CZTcrystal. The 2 ASICs share a common output and transmit the data to ‘ADCPCB’ (C) that handles four ‘CZT MODULES’ (B) in parallel. Thus, a totalof 1024 pixels are presently channeled through one ADC board. The systemis capable of further increasing the accepted event rate by channelingevery two ASICS through a single ADC. The ‘ADC PCB’ (C) transmits thedata to the ‘NRG PCB’ (D) that handles ten ‘ADC PCB’s (C) in parallel,but could be further replicated should one want to further decrease“dead time”. The ‘NRG PCB’ (D) transmits the data to the ‘PC’ (E) whereit is stored.

All in all, in the present embodiment, forty CZT MODULEs which contain atotal of 10240 pixels transmit in parallel to the PC.

The bottle neck, and hence the only constraint, of the system data flowis the ASICS in the ‘CZT MODULE’ (B) and the connection to the ‘ADC PCB’s (C):

1. An ASIC (128 pixels) can process one photon hit within 3.5 uSec, or285,000 events/sec over 128 pixels, i.e. over 2200 events/px/sec-anexceedingly high rate.

2. Two ASICS share the same output, and hence coincident event output ofthe two ASICS in a ‘CZT MODULE’ (B) will cause a collision andinformation loss. The duration of an event output from the ASIC is 1uSec.

When the readout is rapid, the rate at which the radiation emission datais read out of the single-pixel detectors 14 may be greater than therate at which it may be output to the processor. One known solution formanaging a difference data arrival and data processing rates is to use abuffer. The buffer provides temporary storage of the incoming data,which is retrieved at a later time.

A buffered readout configuration can result in the loss of timinginformation, unless active steps are taken to preserve the timeinformation associated with the collected emission data, for example, astaught hereinabove, under the heading, “The Timing Mechanism 30.”

In accordance with embodiments of the present invention, timinginformation is preserved. The electrical scheme may include a bufferwhich stores emission data along with timing information for each dataitem or group of data items (in the case where emission data fromseveral detectors was obtained at substantially the same time, forexample due to parallel readout), and an identification of theassociated detector unit. Utilizing a buffer ensures that emission datamay be collected from the detectors frequently enough to avoidsaturation, even when the data channel throughput is limited. In stopand shoot mode, for example, the emission count data may be stored inthe buffer for retrieval while the detector head is moving to the nextlocation. Accurate reconstruction may thus be performed.

The camera readout circuitry is preferably designed to provide fastreadout and detecting unit discharge. Fast readout circuitry may includefast analog and digital circuitry, fast A/D converters, pipelinedreadout, and so forth.

After the emission data has been read out of the single-pixel detectors14, it may be necessary to convey the data to a processor forreconstruction as a single or limited number of data streams. The cameraelectronic scheme may include a multiplexer, for combining two or moreemission data streams into a single data stream. The emission data maythus be conveyed to the processor over one physical link (or alternatelyover a reduced number of parallel links). For each radioactive emissionevent, the multiplexer includes both the timing information and anidentification of the single-pixel detector 14 supplying the event. Themultiplexed data may later be de-multiplexed by the processor, andreconstruction may be performed with complete information for each dataitem, including for example, total counts per single-pixel detector 14,per time bin, single-pixel detector location and orientation, and thetime bin. Parallel readout may thus be performed, even when thecollected data is to be output over a single data link.

Sensitivity Consideration

It will be appreciated that dynamic imaging with a SPECT camera has beenattempted in the past, unsuccessfully, primarily, because prior-artSPECT cameras are not sensitive enough to provide tomographicreconstruction images, for example, of a heart, with sufficient objectresolution, for example, 10×10×10 cubic millimeters, in less than aminute.

As a case in point, U.S. Pat. No. 7,026,623, to Oaknin, et al., filed onJan. 7, 2004, issued on Apr. 11, 2006, and entitled, “Efficient singlephoton emission imaging,” describes a method of diagnostic imaging in ashortened acquisition time for obtaining a reconstructed diagnosticimage of a portion of a body of a human patient who was administeredwith dosage of radiopharmaceutical substance radiating gamma rays, usingan Anger Camera and SPECT imaging. The method includes effectiveacquisition times from less than 14 minutes to less than 8 minutes.Oaknin, et al., do not claim an effective acquisition time of less than7 minutes. Yet, in view of the section entitled, “Time ScaleConsiderations,” hereinabove, a sampling rate of 8 about minutes is fartoo slow for myocardial perfusion studies, where a sampling rate of atleast two tomographic reconstruction images per heartbeat, that is,about every 30 seconds, is desired, and furthermore, where processesoccur at rates of several seconds, and must be sampled at rates of asecond or less, as seen in FIG. 5B.

The dynamic SPECT camera 10 in accordance with embodiments of thepresent invention achieves sensitivity sufficient for the requiredsampling rates of between every 30 seconds and every half a second, bycombining several features, specifically intended to increasesensitivity, as follows:

a collimator 16 with a solid collection angle δ of at least 0.005steradians or greater, for a fast collection rate, and high sensitivity,wherein the loss in resolution is compensated by one or a combination ofthe following factors:

i. motion in a stop and shoot acquisition mode, at very smallincremental steps, of between about 0.01 degrees and about 0.75 degrees.

ii. simultaneous acquisition by the assemblies 20, each scanning thesame region of interest from a different viewing position, thusachieving both shorter acquisition time and better edge definitions.

iii. the structure 15 conforming to the body contours, for acquisitionwith substantial contact or near contact with the body.

Definition of a Clinically-Valuable Image

In consequence, the dynamic SPECT camera 10 is capable of producing a“clinically-valuable image” of an intra-body region of interest (ROI)containing a radiopharmaceutical, while fulfilling one or more of thefollowing criteria:

1. the dynamic SPECT camera 10 is capable of acquiring at least one of5000 photons emitted from the ROI during the image acquisitionprocedure, such as at least one of 4000, 3000, 2500, 2000, 1500, 1200,1000, 800, 600, 400, 200, 100, or 50 photons emitted from the ROI. Inone particular embodiment, the camera is capable of acquiring at leastone of 2000 photons emitted from the ROI during the image acquisitionprocedure;

2. the dynamic SPECT camera 10 is capable of acquiring at least 200,000photons, such as at least 500,000, 1,000,000, 2,000,000, 3,000,000,4,000,000, 5,000,000, 8,000,000, or 10,000,000 photons, emitted from aportion of the ROI having a volume of no more than 500 cc, such as avolume of no more than 500 cc, 400 cc, 300 cc, 200 cc, 150 cc, 100 cc,or 50 cc. In one particular embodiment, the camera is capable ofacquiring at least 1,000,000 photons emitted from a volume of the ROIhaving a volume of no more than 200 cc;

3. the dynamic SPECT camera 10 is capable of acquiring an image of aresolution of at least 7×7×7 mm, such as at least 6×6×6 mm, 5×5×5 mm,4×4×4 mm, 4×3×3 mm, or 3×3×3 mm, in at least 50% of the reconstructedvolume, wherein the radiopharmaceutical as distributed within the ROIhas a range of emission-intensities I (which is measured as emittedphotons/unit time/volume), and wherein at least 50% of the voxels of thereconstructed three-dimensional emission-intensity image of the ROI haveinaccuracies of less than 30% of range I, such as less than 25%, 20%,15%, 10%, 5%, 2%, 1%, or 0.5% of range I. For example, theradiopharmaceutical may emit over a range from 0 photons/second/cc to10^5 photons/second/cc, such that the range I is 10^5 photons/second/cc,and at least 50% of the voxels of the reconstructed three-dimensionalintensity image of the ROI have inaccuracies of less than 15% of rangeI, i.e., less than 1.5×10⁴ photons/second/cc. For some applications, thestudy produce a parametric image related to a physiological processoccurring in each voxel. In one particular embodiment, the image has aresolution of at least 5×5×5 mm, and at least 50% of the voxels haveinaccuracies of less than 15% of range I;

4. the dynamic SPECT camera 10 is capable of acquiring an image, whichhas a resolution of at least 7×7×7 mm, such as at least 6×6×6 mm, 5×5×5mm, 4×4×4 mm, 4×3×3 mm, or 3×3×3 mm, in at least 50% of thereconstructed volume, wherein the radiopharmaceutical as distributedwithin the ROI has a range of emission-intensities I (which is measuredas emitted photons/unit time/volume), and wherein at least 50% of thevoxels of the reconstructed three-dimensional emission-intensity imageof the ROI have inaccuracies of less than 30% of range I, such as lessthan 25%, 20%, 15%, 10%, 5%, 2%, 1%, or 0.5% of range I. For example,the radiopharmaceutical may emit over a range from 0 photons/second/ccto 10⁵ photons/second/cc, such that the range I is 10⁵photons/second/cc, and at least 50% of the voxels of the reconstructedthree-dimensional intensity image of the ROI have inaccuracies of lessthan 15% of range I, i.e., less than 1.5×10⁴ photons/second/cc. For someapplications, the study produces a parametric image related to aphysiological process occurring in each voxel. In one particularembodiment, the image has a resolution of at least 5×5×5 mm, and atleast 50% of the voxels have inaccuracies of less than 15% of range I;

5. the dynamic SPECT camera 10 is capable of acquiring an image, whichhas a resolution of at least 20×20×20 mm, such as at least 15×15×15 mm,10×10×10 mm, 7×7×7 mm, 5×5×5 mm, 4×4×4 mm, 4×3×3 mm, or 3×3×3 mm,wherein values of parameters of a physiological process modeled by aparametric representation have a range of physiological parameter valuesI, and wherein at least 50% of the voxels of the reconstructedparametric three-dimensional image have inaccuracies less than 100% ofrange I, such as less than 70%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5%,2%, 1%, or 0.5% of range I. For example, the physiological process mayinclude blood flow, the values of the parameters of the physiologicalprocess may have a range from 0 to 100 cc/minute, such that the range Iis 100 cc/minute, and at least 50% of the voxels of the reconstructedparametric three-dimensional image have inaccuracies less than 25% ofrange I, i.e., less than 25 cc/minute. In one particular embodiment, theimage has a resolution of at least 5×5×5 mm, and at least 50% of thevoxels have inaccuracies of less than 25% of range I; and/or

6. the dynamic SPECT camera 10 is capable of acquiring an image, whichhas a resolution of at least 7×7×7 mm, such as at least 6×6×6 mm, 5×5×5mm, 4×4×4 mm, 4×3×3 mm, or 3×3×3 mm, in at least 50% of thereconstructed volume, wherein if the radiopharmaceutical is distributedsubstantially uniformly within a portion of the ROI with anemission-intensity I+/−10% (which is defined as emitted photons/unittime/volume), and wherein at least 85% of the voxels of thereconstructed three-dimensional emission-intensity image of the portionof the ROI have inaccuracies of less than 30% of intensity I, such asless than 15%, 10%, 5%, 2%, 1%, 0.5%, 20%, or 25% of intensity I. Forexample, the radiopharmaceutical may be distributed within a volume witha uniform emission-intensity I of 10^5 photons/second/cc, and at least85% of the voxels of the reconstructed three-dimensional intensity imageof the volume have inaccuracies of less than 15% of intensity I, i.e.,less than 1.5×10⁴ photons/second/cc. For some applications, the samedefinition may apply to a study which produces a parametric imagerelated to a physiological process occurring in each voxel. In oneparticular embodiment, the image has a resolution of at least 5×5×5 mm,and at least 50% of the voxels have inaccuracies of less than 15% ofintensity I.

It is expected that during the life of this patent many relevant dynamicSPECT cameras will be developed and the scope of the term dynamic SPECTcamera is intended to include all such new technologies a priori.

As used herein the term “substantially” refers to ±10%.

As used herein the term “about” refers to ±30%.

Additional objects, advantages, and novel features of the presentinvention will become apparent to one ordinarily skilled in the art uponexamination of the following examples, which are not intended to belimiting. Additionally, each of the various embodiments and aspects ofthe present invention as delineated hereinabove and as claimed in theclaims section below finds experimental support in the followingexamples.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

1. A method for anatomic construction of voxels, comprising: providing a structural image of a region of interest; constructing an anatomic system of voxels, for the region of interest, in which voxel boundaries are aligned with boundaries of structural objects of the region of interest, based on the structural image; performing radioactive-emission imaging of the region of interest, utilizing the anatomic system of voxels; performing reconstruction of the radioactive-emission imaging, utilizing the anatomic system of voxels; and fitting the boundaries of the structural objects to parametric equations and utilizing the parametric equations in the constructing of the anatomic system of voxels.
 2. The method of claim 1, wherein the structural image is provided by a structural imager, selected from the group consisting of 2-D ultrasound, 3-D ultrasound, planner x-rays, CT x-rays, and MRI.
 3. The method of claim 2, wherein the structural imager is co-registered to a radioactive-emission imaging camera which performs the radioactive-emission imaging.
 4. The method of claim 3, and further including attenuation correction of the radioactive-emission imaging based on the structural image.
 5. The method of claim 3, and further including displaying the structural image and the reconstruction of the radioactive-emission imaging together.
 6. The method of claim 2, wherein the structural imager is not co-registered to a radioactive-emission imaging camera which performs the radioactive-emission imaging, and further including corrections for misregistration.
 7. The method of claim 1, wherein the structural image is provided from a lookup system.
 8. The method of claim 7, wherein the lookup system is corrected for patient's details.
 9. A method for anatomic construction of voxels, comprising: providing a structural image of a region of interest; constructing an anatomic system of voxels, for the region of interest, in which voxel boundaries are aligned with boundaries of structural objects of the region of interest, based on the structural image; performing radioactive-emission imaging of the region of interest, utilizing the anatomic system of voxels; and performing reconstruction of the radioactive-emission imaging, utilizing the anatomic system of voxels; wherein the anatomic system of voxels includes voxels of varying volumes, depending on their anatomic position and relevance.
 10. A method for anatomic construction of voxels, comprising: providing a structural image of a region of interest; constructing an anatomic system of voxels, for the region of interest, in which voxel boundaries are aligned with boundaries of structural objects of the region of interest, based on the structural image; performing radioactive-emission imaging of the region of interest, utilizing the anatomic system of voxels; performing reconstruction of the radioactive-emission imaging, utilizing the anatomic system of voxels; and time- binning of the radioactive emissions to time periods not greater than substantially 30 seconds.
 11. A method for anatomic construction of voxels, comprising: providing a structural image of a region of interest; constructing an anatomic system of voxels, for the region of interest, in which voxel boundaries are aligned with boundaries of structural objects of the region of interest, based on the structural image; performing radioactive-emission imaging of the region of interest, utilizing the anatomic system of voxels; and performing reconstruction of the radioactive-emission imaging, utilizing the anatomic system of voxels; wherein the anatomic system of voxels includes voxels of varying volumes, depending on the relevance of their dynamic activity.
 12. A method of reconstruction of a radioactive emission image, comprising: providing a first system of voxels for a region of interest; obtaining radioactive-emission data from the region of interest; performing a first reconstruction, based on the radioactive-emission data and the first system of voxels, to obtain a first image; correcting the first system of voxels, by aligning voxel boundaries with object boundaries, based on the first image; thus obtaining a second system of voxels; performing a second reconstruction, based on the radioactive-emission data and the second system of voxels, thus obtaining a second image.
 13. A dynamic SPECT camera configured for dynamically determining a spectral energy bin for each detecting unit, the camera comprising: an overall structure, which defines proximal and distal ends with respect to a body; a plurality of detecting unit; arranged on the overall structure and configured for detecting radioactive emissions in a spectral range between 10 KeV and 1 MeV; a spectral selection mechanism, for enabling a selection of a spectral energy bin to be used for each detecting unit, independently from the other detecting units; and a lookup system of recommended spectral energy bin values, as functions of at least one of a specific region of interest, an administered radiopharmaceutical, time since the administration of the radiopharmaceutical, a view of the detecting unit with respect to the region of interest, and patient's details; wherein the spectral selection mechanism is further configured for dynamically determining the spectral energy bin for each detecting unit, as functions of at least one of the specific region of interest, the administered radiopharmaceutical, the time elapsed since the administration of the radiopharmaceutical, the view of the detecting unit with respect to the region of interest, and patients' details, from the lookup system.
 14. The dynamic SPECT camera of claim 13, wherein the spectral energy bin is designed to include a primary photon energy ±10%.
 15. The dynamic SPECT camera of claim 13, wherein the spectral energy bin is designed to include a primary photon energy ±7%.
 16. The dynamic SPECT camera of claim 13, wherein the spectral energy bin is designed to include a primary photon energy ±5%.
 17. The dynamic SPECT camera of claim 13, and further including administering at least two radiopharmaceuticals and viewing a same region with different groups of detecting units, each group being configured for a different spectral energy bin, so as to view each radiopharmaceutical in the same region independently of the other.
 18. The dynamic SPECT camera of claim 13, wherein the spectral selection mechanism is a hardware unit.
 19. The dynamic SPECT camera of claim 13, and further including: a first plurality of assemblies, arranged on the overall structure, forming an array of assemblies, each assembly comprising: a second plurality of the detecting units, each of the detecting units including: a single-pixel detector, for detecting radioactive emissions; and a dedicated collimator, attached to the single-pixel detector, at the proximal end thereof, for defining a solid collection angle δ for the detecting unit; and an assembly motion provider, configured for providing the assembly with individual assembly motion with respect to the overall structure, during the acquisition of radioactive-emission data for a tomographic image. 